The camera has a long history as a means to record visual information. As of recent, digital cameras which perform digital encoding of images captured with a solid state imaging device such as a CCD (Charge Coupled Device) or CMOS (Complementary Mental-Oxide Semiconductor) or the like has become widespread, replacing silver-salt cameras which take pictures using film or photosensitive plates. Digital cameras are advantageous in that images subjected to digital encoding are stored in memory and image processing and image management can be performed by computer, and further, that there is no problem of the life expectancy of film. Currently, many digital still cameras, digital video cameras, digital cameras implemented in cellular phones and PDAs (Personal Digital Assistants), and monitoring cameras, use solid state devices.
Either imaging devices of CCD and CMOS are configured with an arrangement wherein two-dimensionally arrayed pixels (photodiodes) use photoelectric effect to convert light into electric charge. The surface of each pixel has a color pixel of one of three colors of R (red), green (G), blue (B), for example, and signal charge corresponding to the amount of incident light passing through each color filter is accumulated in each pixel. The color filters are band-pass filters which pass light of a predetermined wavelength. Signal charges according to the amount of incident light of each color are read out from each pixel, and the color of incident light at each pixel position can be reproduced from the amount of signal charge of each of the three colors.
As of recent, with the advance in miniaturization technology, higher resolution of imaging devices has advanced. However, miniaturizing pixels due to high resolution leads to the concern that sensitivity will decrease due to decrease in the amount of charge accumulated at each pixel. One method that has been proposed to realize high sensitivity is color coding of an array including “white (WHITE) pixels) that do not include an optical band-pass filter on the pixel (e.g., see NFL 1). High sensitivity pixels such as white pixels have a feature that the sensitivity to incident light is higher as compared to chromatic pixels, and the sensitivity properties can be improved in a low-illuminance environment (e.g., see PTL 1).
FIG. 12A illustrates a Bayer array which is a representative filter array of primary colors. Also, FIG. 12B illustrates an example of a filter array including white pixels. Here, in the drawing, R represents Red (red) color filters, G represents Green (green) color filters, B represents Blue (blue) color filters, and W represents White (white) color filters, respectively. In the example illustrated in the drawing, white pixels are introduced between the RGB primary color system color filters in an intermittent manner.
Also, with miniaturization of pixels, there is concern that optical and electrical crosstalk, i.e., color mixing (hereinafter referred to simply as “crosstalk”) will occur between adjacent. Factors of crosstalk include leaking of light which should be collected at the adjacent pixel, electrons leaking between pixels, and so forth.
Crosstalk leads to deterioration in resolution and loss of color information, and accordingly needs to be corrected. Now, crosstalk is not a problem unique to imaging devices using color filters including white pixels in the array.
However, a greater amount of light leaks from white pixels, so deterioration of images due to crosstalk is more marked as compared to imaging devices using color filters not including white pixels in the array.
Even with the same imaging device, the amount of crosstalk varies depending on optical conditions such as individual micro-lenses. This is because crosstalk is dependent on the incident angle. Accordingly, the amount of crosstalk differs depending on the position of the pixels on the chip face. Also, the depth of penetration into the silicon (Si) substrate configuring the imaging device differs depending on the wavelength of the light, so the amount of crosstalk also changes depending on the color temperature of the light source at the time of shooting.
For example, a signal processing method has been proposed which handles change in crosstalk owing to optical conditions, by performing corresponding processing as to signals of a pixel of interest using signals of each of multiple surrounding pixels adjacent to a pixel of interest of the imaging device, and correction parameters set independently for each of the signals (e.g., see PTL 2). However, with this signal processing method, the values of the correction parameters are set in accordance with the aperture of the diaphragm included in the optical system guiding light from the subject to the imaging device. That is to say, the lens to be used is already decided, the amount of crosstalk according to the lens has been measured beforehand, and correction is performed as to this. Accordingly, correction of the amount of crosstalk is difficult with a situation where lens information is unknown, such as with exchangeable lenses wherein the user can freely exchange lenses.